Alberto Contador: How strong is the doping case against him?

The Spanish superstar blamed the traces, which were 400 times below what accredited labs must be able to detect, as coming from meat he had consumed the previous evening – a claim supported by Dutch doctor Douwe de Boer, who provided an opinion at the request of Contador's attorney.

That would have been the night after Contador, a renowned climber, finished nearly seven minutes out of the lead on the first of two trips up the race's most notorious climb, the Col du Tourmalet. After the rest day, when the drug was detected, he and rival Schleck dusted the entire field in a strenuous rematch up the Col du Tourmalet, which Schleck won by half a length.

In a detailed opinion, Dr. Boer argues that given the short half-life of the drug and the fact that no traces of it showed up in Contador’s July 19 or 20 tests, the cyclist must have ingested it on the night of July 20. He also says clenbuterol – an anabolic agent used mainly to treat asthma – is sometimes used illegally as a growth agent for cattle. If humans eat such meat, the substance can show up in their system.